1. Field of the Invention
Embodiments of the present invention relate to a die clamping unit for dies, more particularly to a die clamping unit which performs a core-back operation in an injection molding process.
2. Description of the Related Art
A core-back operation is performed in a molding process in a case where a material mixed with a foaming agent is used, for example, in an injection molding machine or the like. The core-back refers to an operation in which a movable platen provided with a movable die is moved backward at a low speed wherein large part of a material is molten. Here, to move backward the movable platen indicates the moving of the movable platen in a direction away from a stationary platen. According to this core-back operation, a pressure in dies is lowered, and foaming of the foaming agent is promoted. A die clamping unit which performs this type of core-back is described in for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-314492.
In the core-back operation, the movable platen is moved by, for example, a servomotor. In the core-back operation, an inertial force develops on the movable platen with the movement of the movable planten. Therefore, even if the drive of the servomotor is stopped at completion of the core-back, the movable platen often continues to move under its own inertia.
During the core-back, a back pressure is applied to a die clamping unit via a hydraulic die clamping cylinder. The back pressure is a pressure that generates a force in a direction opposite to a moving direction of the movable platen.